Polyamide resins are widely used as engineering plastics having excellent mechanical strength such as impact resistance and friction/abrasion resistance as well as excellent heat resistance and oil resistance in the fields of automotive parts, electronic/electric equipment parts, office automation equipment parts, machine parts, construction materials/housing parts and the like, and recently have found increasingly wide applications.
Many classes of polyamide resins including e.g., polyamide 6 and polyamide 66 are known, among which m-xylylene adipamide (hereinafter sometimes referred to as “MXD6”) derived from m-xylylenediamine and adipic acid is positioned as a very excellent polyamide resin because it contains an aromatic ring in the main chain unlike polyamide 6 and polyamide 66 so that it has high rigidity, low water absorption and excellent oil resistance as well as a low shrinkage ratio during molding and causes little shrinkage or warp, which means that it is also suitable for precision molding. Thus, MXD6 has recently been more widely used as a molding material, especially extrusion molding material in various fields including electronic/electric equipment parts, parts of vehicles such as automobiles, general machine parts, precision machine parts, leisure/sports goods, civil engineering and construction materials, etc.
Lighter and stronger polyamide resin materials are also needed and a known xylylene polyamide resin lighter than MXD6 includes a xylylene sebacamide polyamide resin derived from xylylenediamine and sebacic acid (hereinafter sometimes referred to as “XD10”) (see patent document 1), which has been highly expected as a material for various parts because of its excellent chemical resistance and impact resistance especially in recent years.
On the other hand, various methods for melt-blending MXD6 with other polyamide resins having high flexibility such as polyamide 6 and polyamide 66 have been proposed to meet increasingly growing commercial needs of recent years in applications requiring high impact resistance or flexibility (e.g., see patent documents 2 and 3). However, the melt viscosity may increase above the arithmetic mean when a polyamide resin containing an m-xylylene group is melt-blended with another polyamide resin. As a means for avoiding this phenomenon, a polyamide resin having a terminal group ratio of carboxyl groups in excess over amide groups has been proposed to prevent the progress of amidation in the molten state (patent document 4). Especially for the purpose of preventing gelling of MXD6, polyamide resins having a low amino group concentration have been proposed. For the purpose of improving the flexibility of MXD6, a polyamide having a specific difference between the carboxyl group concentration and the amino group concentration has also been proposed by copolymerizing ε-caprolactam (patent document 5), but it was insufficient in physical properties for use in injection molding.
Incorporation of an elastomer into MXD6 or XD10 for the purpose of increasing elongation may be a promising means for providing high impact resistance or flexibility. However, simple incorporation of an elastomer into XD10 disadvantageously tends to cause insufficient dispersion of XD10 and the elastomer, which may result in a decrease in the intrinsic rigidity or impact resistance.
Thus, there have been high demands for developing XD10 polyamide resins capable of achieving high impact resistance and high flexibility by simply adding an elastomer.
Further, polyamide resins are required to have a low YI. Especially, an increase in YI after heating should be reduced.